The present invention relates to a method and apparatus for upsetting and end portion of a rough forged bar to form a blank from which a turbojet engine compressor vane may be manufactured.
Turbojet engine compressor vane blanks have been manufactured by upsetting the end of a cylindrical bar to increase the cross sectional area of the bar to a required volume of material to make the root of the compressor vane. Limits on the upsetting procedure can be defined by two kinds of parameters:
(a) Technical parameters, such as the upsetting ratio t defined by t=(L.sub.0 -L.sub.0)/D.sub.0 wherein L.sub.0 is the initial length of the portion of the bar being upset, L.sub.1 is the length of the bar portion after upsetting and D.sub.0 is the initial diameter of the bar being upset. L.sub.0 -L.sub.1 is the effective path of the forge punch being used, the upper limit of this path being a design feature of a particular forge; and,
(b) Metallurgical parameters such as the reduction ratio r defined by r=L.sub.0 /L.sub.1 =S.sub.1 /S.sub.0 =(D.sub.1 /D.sub.0).sup.2 in which S.sub.0 is the initial cross sectional area of the bar, S.sub.1 is the final cross section of the bar following the upsetting procedure and D.sub.1 is the corresponding diameter.
Geometric restrictions have been placed on the known upsetting methods to avoid unacceptable defects in the formed blanks. The defects are caused by inadequate control of the bar deformation during the upsetting process and typically consist of folds which may be caused by buckling of the bar segment or improper fiber orientation due to the twisting of the bar after buckling. The defects imposed upon the bar by the known methods are illustrated in FIGS. 1a, 1b, 1c and 1d. In these figures, a bar B is placed in a die A to upset an end portion of the bar in a 4-step operation. The individual steps are represented by the figures and result in length reductions l.sub.1, l.sub.2, l.sub.3 and l.sub.4. The bar B may buckle and then twist during the length reductions leading to the known defects noted above.
It is conventionally thought that, in order to avoid these defects, upper limits must be placed on the upsetting ratio and the reduction ratio. Generally, an upper limit of 4 has been placed on the upsetting ratio t in regard to a single operation upsetting method, or an upper limit of 6 when a 2-step upsetting method is utilized. An upper limit of the reduction ratio r of between 1.5 and 2 has been used, depending upon the type of alloy of the bar.
Various attempts have been made to exceed these upper limits without forming the aforementioned defects. Upsetting has been carried out by a tool nutating on the bar end in which the bar is simultaneously displaced toward the work zone by a length corresponding to the volume to be formed. Also, upsetting in several passes has been attempted by advancing the bar at each pass by the length related to the volume to be formed. Such typical examples of these methods can be found in French patents Nos. 2,050,483; 2,050,484; and 2,220,328. While these procedures have been an improvement, they have not satisfactorily eliminated the known defects, in particular, the fiber orientation has proven to be unreliable.